1. Field of the Invention
This invention relates to a memory locking means for an electric shutter in a photographic camera, and more particularly to a means for locking a memorized value in a memory element in a digital control type electric shutter for a photographic camera. The memory locking means in accordance with the present invention is also applicable to a diaphragm control device for a photographic camera wherein the aperture size of a diaphragm is electrically controlled.
2. Description of the Prior Art
In the conventional electric shutter or a diaphragm control device for a photographic camera, the shutter speed or the aperture size of the diaphragm is controlled in accordance with a terminal voltage of a memory capacitor provided in the camera. This type of shutter speed or diaphragm control device (hereinafter referred to as "exposure control device") suffers from a defect that the capacitor used for memorizing exposure information is automatically charged with the voltage at a predetermined moment. For instance, the exposure information is memorized and locked immediately before the swing-up of a swingable mirror in the camera. For example, as shown in U.S. Pat. No. 3,995,284 to Kitaura, the exposure information is memorized immediately before the shutter release operation. Therefore, the exposure is always controlled based on the scene brightness measured immediately before release of the shutter. This means that the exposure is always controlled as faithfully as possible to the actual scene brightness.
In the above described conventional exposure control device, it is impossible to automatically obtain desirable exposure for a special object illuminated by abnormal illumination, e.g. an object in the back-light, an object in the spot-light, etc.